Routing Protocol Basics

Interior Gateway Protocols (IGPs) and Exterior Gateway Protocols (EGPs)

What are two types of routing protocols that are used in internetworks?

Interior Gateway Protocols (IGPs)

These protocols are used to exchange routing information with routers in the same autonomous system (AS).

Autonomous System (AS)

An a collection of networks under a common administrative domain, which simply means that all routers sharing the same routing table information are in the same AS.

Exterior Gateway Protocols (EGPs)

These protocols are used to communicate between multiple ASs. A nice example of an EGP would be Border Gateway Protocol (BGP).

Administrative Distance (AD)

A number that is used by routing protocols to determine the trustworthiness of a route. If two route updates are received on a router with different of these, the router will accept only the one with the lower number and discard the other route update.

Distance Vector, Link-State, and Hybrid Protocols

What are the three classes of routing protocols?

Distance Vector Protocols

The class protocols find the best path to a remote network by judging—you guessed it—distance. The vector indicates the direction to the remote network. RIP, RIPv2, and Interior Gateway Routing Protocol (IGRP) are this class of routing protocols.

Link-State Protocols

Using this class of protocols, also called shortest path first protocols, the routers each create three separate tables. One of these tables keeps track of directly attached neighbors, one determines the topology of the entire internetwork, and one is used as the actual routing table. Routers of this class know more about the internetwork than any distance-vector routing protocol. OSPF and IS-IS are IP routing protocols that are completely link state.

Hybrid Protocols

This class of protocols uses aspects of both distance vector and link state. EIGRP and BGP (or iBGP) are hybrid protocols.